Common analog telephone communications devices allow users to exchange audio information via analog signals over a pair of analog transmission wires extending between a telephone network's central office (CO) equipment and the subscriber's (telephone user's) premises and, if necessary, trunk lines between COs. The wires are known in the art as a subscriber loop.
Digital data from modern computer systems may be transmitted over analog lines using analog modulator-demodulators (modems). A modulator converts a digital signal to a corresponding analog signal (e.g., a tone) that may be transmitted over the subscriber loop of a plain old telephone system (POTS). A demodulator converts the analog signal back to the corresponding digital signal. Modems are now commonly connected to "personal computers" (PC) to enable PCs to transfer digital information over POTS. Unfortunately, these modems are typically restricted to transmitting a narrow data bandwidth.
Fiber optic communication systems are a recently developing technology that display many benefits over POTS. The fiber optic systems transmit information faster, are more reliable, and can carry signals having a greater bandwidth than POTS. The fiber optic systems can transmit signals over great distances with less signal strength loss or signal distortion than POTS. POTS do exhibit some benefits over fiber optic systems including the relative high expense of fiber optic systems. Additionally, in most developed nations, POTS already exist while fiber optic systems must be installed. Thus, there are large incentives to improve and develop existing POTS systems.
The integrated services digital network (ISDN) protocol has a basic rate interface version (ISDN BRI) that provides for the transmission of data and voice signals using the POTS subscriber loop. ISDN BRI can carry a greater bandwidth over subscriber loops than POTS can carry over subscriber loops. The transmission equipment required for ISDN BRI is referred to as the digital subscriber loop (DSL). ISDN BRI comprises two 64 KBit/second bearer (ISDN B) channels for transmitting voice, data, etc. and one 16 KBit/second data (ISDN D) channel for transmitting signaling data or packet-switching (in the United States). Thus, ISDN BRI is also commonly referred to as 2B+D access.
ISDN also has a primary rate interface (ISDN PRI) version that can carry a greater bandwidth than ISDN BRI utilizing modified subscriber loop technology. PRI includes 23 ISDN B channels and one ISDN D channel (23B+D). In Europe, ISDN PRI has 30 ISDN B channels and one ISDN D channel (30B+D). ISDN narrowband comprise ISDN BRI and ISDN PRI. Asynchronous transfer mode (ATM) protocol is a well-known broadband version of ISDN, and is sometimes referred to as "broadband ISDN".
Two ISDN interfaces are especially applicable to the present invention; the ISDN U interface and the ISDN S/T interface. In the United States, ISDN BRI service is provided via the network "U interface" by a connection to the subscriber's network termination apparatus (NT). The U interface is specified in the American National Standard for Telecommunication publication entitled, "Integrated Services Digital Network (ISDN)--Basic Access Interface for use on Metallic Loops for Application on the Network side of the NT (LAYER 1 Specification)", also known as ANSI T1.601. The ANSI T1.601 specification describes the physical interface located between a line termination (LT) side of the DSL (that is located at the CO), and a Network Termination (NT) side of the DSL (that is located at the subscriber's premises).
The U interface is a two-wire subscriber loop providing point-to-point communication only. That is, only one device (having an embedded U interface termination) may be attached directly to each U interface. If the terminal equipment is provided with an embedded U interface connection and is connected to the subscriber loop, no additional terminals may be connected to the U interface.
Unlike the U interface, the S/T interface (specified by the International Telecommunications Union T Recommendation I.430, ITU-T Recommendation I.430, and ANSI T1.605 in North America) enables connecting multiple terminal equipment to the ISDN U interface at the customer premises. ISDN S/T interface connections are provided in Europe where the NT apparatus is considered the property of the local phone company. The device that converts the U interface to the S/T interface is referred to as a Network Termination Type 1 (NT1) interface device. The NT1 interface device is an active electronic device known by those skilled in the art. The U-interface allows the terminal apparatus to communicate with a central office, while the S/T interface permits terminals to be connected to the network.
As computer networks become more numerous and elaborate, there will be a greater number of network interfaces. One such interface is the peripheral component interconnect (PCI) contained in most personal computers (PC). Network interface cards (NIC) are add-on cards that enable computers to be attached to a network. A variety of network interface cards (NIC) are configured to connect with the computers at the PCI. As network deployment increases, the NIC market has exploded. Devices connected via NIC connections have been relatively simple at this time, such as fax machines, modems, or other peripherals. As networks expand, and the associated computers are called upon to perform more tasks for more end users, it is expected that the NICs will provide more functionality.
Telephones are now able transmit voice information using a computer network. Each computer connected to a telephone requires a separate. To connect a telephone to a computer, the phone portion converts the analog voice signal into a digital signal that may be processed and carried to a remote telephone. Long distance telephone calls may be made over the Internet while paying relatively low Internet access rates.
In general, computers being able to process multiple varied types of audio, video, and data based information is referred to as multimedia. As multimedia computer characteristics increase, there is be a trend to connect more, and an increased variety of, devices to computers. This connection of multiple varied devices to computers may tend to overburden the computer processor. Under extreme cases, the computer may not be able to run at all.
Many computers are configured to carry a limited number of interfaces. If a computer is attached to an ISDN connection, this may limit the other peripherals or communication links that connect to the computer. It may be desirable to provide a computer interface that can connect to multiple connection links. In addition, adding many interfaces, and software associated with the interfaces, to a computer may slow down the computer processor especially for computers having less powerful processors and computers not configured for multimedia applications.
The interfaces associated with computers throughout the world vary considerably. ISDN interfaces are no exception. For instance, in the United States, ISDN PRI comprises 23 ISDN B channels and one ISDN D channel; while in Europe, ISDN PRI comprises 30 ISDN B channels and one ISDN D channel. Ring cadence is a measure of the ring timing characteristics of a telephone (for example, the phone rings for a prescribed period then is silent for another prescribed period). Ring cadence is typically standardized in telephones of the same country, but varies from country to country. Ring frequency is a measure of the frequency that a telephone rings at. Ring frequency is also typically standardized in telephones of the same country, but varies from country to country.
Considering that NICs have the potential to be distributed in different countries throughout the world, it might be desired to provide a NIC that could adapt to the ISDN, telephone, and/or modem peculiarities of each country in which it is likely to be used. It might also be desired to provide a communication system that could provide either modem communications or ISDN communications as selected by an end user of the computer. It might be desired to provide a system that could interact with a variety of ISDN interfaces utilizing the PCI. It might be desired to provide an interface that, by itself, has multiple interfaces to distinct devices or communication systems. It might finally be desired to be able to provide an interface for multiple, possibly diverse, devices without requiring the computer to do all of the processing associated with the multiple interfaces.